Electrostatic copying machine

ABSTRACT

A copying machine for making large numbers of xerographic copies by first forming an electrostatic image of the subject matter to be copied on a first carrier unit, and then making a series of electrostatic images from that first image on a second unit, and printing a series of copies of the subject matter on successive copy sheets by the second unit. Retention of the initial image on the first electrostatically chargeable unit enables removal of the original sheet to be copied from the machine while the reproductions thereof are still being produced. A mechanism is also provided to maintain constant the optical path length of a tilting mirror photoreproduction device with flat platten during the tilting of the mirror.

United States Patent [191 Miller Aug. 14, 197.3

ELECTROSTATIC COPYING MACHINE inventor: Wendell S. Miller, 1341 Cornstock Ave., Los Angeles, Calif. 90024 Filed: Apr. 29, 1971 Appl. No.: 138,449

References Cited UNITED STATES PATENTS Primary Emnulnw-Fred L. Bmtm Azzomey-william P. Green 5 7 ABSTRACT A copying machine for making large numbers of xerographic copies by first forming an electrostatic image of the subject matter to be copied on a first carrier unit, and then making a series of electrostatic images from that first image on a second unit, and printing a series of copies of the subject matter on successive copy sheets by the second unit. Retention of the initial image on the first electrostatically chargeable unit enables removal of the original sheet to be copied from the machine while the reproductions thereof are still being produced. A mechanism is also provided to maintain constant the optical path length of a tilting mirror photoreproduction device with flat platten during the tilting of the mirror.

16 Claims, 3 Drawing Figures PAIENIEB M18 I4 I975 SHEEI 1 [IF 2 INVENTOR. WE/UDELL 6. M/LLEE TTOQJE V PATENTEBMIGI 14 W5 3.752.573 SHEEI 2 0F 2 INVENT OR. Nzdozu. 6, MMLEQ IQTTQQJEV 1 ELECTROSTATIC COPYING MACNE BACKGROUND OF THE INVENTION This invention relates to improved electrostatic type copying machines.

In the conventional electrostatic copying machines, if it is desired to make a number of copies from a single original, it is necessary to leave the original in the machine during the entire period that all of the copies are being made. In many instances, this necessity for leaving the original in place until the last copy has been made results in a very inefficient expenditure of time, because the person operating the machine must wait until all copies of a particular original have been completed before he can remove that original and place another in the machine for the next copying operation. Further, the original is rendered completely inaccessible for use by others during the entire copying period.

SUMMARY OF THE INVENTION A xerographic machine embodying the present in vention overcomes the above discussed limitation of prior machines by enabling production of a large number of identical copies of a single original without requiring retention in the machine of the original during the entire copying period. More specifically, the original may be left in or on the machine only long enough to form a single electrostatic image of its subject matter, following which the original may be completely removed from the machine and be replaced by another while the machine continues to produce as many printed copies as may be desired of the first original. Thus, greatly increased efficiency of time is attained by enabling the operator to remove one original and replace it by another during the time that the copies of the first are being printed. Further, the period during which each original is rendered inaccessible for use by others is minimized.

These results are achieved by forming a primary electrostatic image of the subject matter to be copied on a first electrostatically chargeable unit, and then subsequently utilizing that first image to form a series of similar electrostatic images on a second chargeable unit by which the actual printing operation is performed. Thus, after the primary image has been formed on the first unit, the sheet being copied may be completely removed from the apparatus, and the second unit be thereafter charged and recharged from the first repeatedly to produce as many identical copies as may be desired. Preferably, the two units are electrostatically chargeable drums, which are driven rotatively in timed relation to one another, and which have portions in close proximity to one another in a relation enabling the charge pattern on the first drum to produce a corresponding charge pattern on the second drum. Each portion of the second drum may be electrically precharged before arrival at the location of close proximity to the other drum, and may then be locally illuminated at that closely proximate location to enable selective discharging of different regions of the second drum in a manner setting up the desired electrostatic charge image. The light for illuminating the second drum at that location may be directed radially outwardly from the interior of the drum.

An additional feature of the invention relates to a unique scanning arrangement by which the optical system of the copy machine scans the sheet which is being copied. As will appear, the scanning apparatus is preferably of a type in which a mirror in the optical system pivots about a predetermined axis in order to scan across the sheet being copied. In the past, apparatus employing such a pivoting mirror has required positioning of the sheet being copied in an arcuately curved condition, in which it curves essentially about the axis of pivotal movement of the mirror. Such curved orientation of the sheet being copied is in many instances extremely inconvenient, particularly where the sheet is a page of a book which cannot be easily held in such curved condition.

The present apparatus enables use of a pivotal mirror of the discussed type without requiring such curvature of the subject matter being copied. To attain this result, the mirror is, during its pivotal movement, also shifted bodily in a direction transversely of the axis of pivotal movement of the mirror, and in a relation enabling proper reproduction of the sheet being copied even though that sheet is in flattened condition. An appropriate camming mechanism may be employed for thus shifting the mirror in timed relation to its pivotal movement.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and objects of the invention will be better understood from the following detailed description of the typical embodiment illustrated in the accompanying drawings in which:

FIG. 1 is a somewhat diagrammatic vertical section through an electrostatic copying machine constructed in accordane with the invention;

FIG. 2 is a greatly enlarged fragmentary representation of the contacting portions of the two drums of FIG. 1; and

FIG. 3 is an enlarged fragmentary perspective view representing the mirror actuating mechanism of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. I, I have illustrated at 10 an electrostatic copying machine embodying the invention and having a housing 11 with a top wall 12 having a transparent horizontal rectangular window 13 over which a sheet or page 14 to be copied is placed in face down condition. The entire underside of sheet 14 is illuminated uniformly in any convenient manner, as by lamps 15 extending about the periphery of the glass forming window 13. The illuminated compartment l6 within the housing is separated from the compartment 17 which contains the bulk of the operating mechanism by an opaque typically metal partition or wall 18, which may have an inclined portion 19 containing a horizontally elongated light passing slit 20.

The subject matter to be copied at the underside of sheet 14 is imaged through slit 20 by an optical projection system 21 typically including a lens 22 and a mirror 23 having an inclined planar reflective surface 123 which reflects an image of sheet 14 along optical axis 24 toward the mirror and ultimately through slit 20 onto an electrostatically chargeable drum 25. Mirror 23 is mounted to pivot about a horizontal axis 26 to progressively scan in a left to right direction across sheet 14, and direct a scanning image of sheet 14 through slit 20 onto drum 25. During such movement, the mirror 23 is also shifted toward and away from slit 20, along optical axis 24, in a manner enabling formation of a proper image on drum even though sheet 14 is in flattened condition and not arcuately curved as is conventional in other pivoted mirror scanning systerns.

In order to enable such bodily shifting movement of mirror 23 along optic axis 24, the mirror may have a horizontal mounting shaft 27 (FIG. 3), rigidly connected to the mirror and projecting in opposite directions therefrom into two parallel inclined guideway slots 28 formed in stationary frame elements 29. Two springs 30 may be connected at 31 to shaft 27 and at their opposite ends 32 be connected to the frame of the machine, to yieldingly urge the shaft 27 and the carried mirror upwardly and leftwardly along optic axis 24 as viewed in FIG. 1. Such upward and leftward movement of the mirror is limited by engagement of a cam surface 33 formed at the back side of the mirror with a roller 34 which is suitably connected to the frame of the machine for rotation about a fixed horizontal axis 35. The contour of cam 33 is predesigned to attain a predetermined positioning of the mirror along optic axis 24 for each position to which the mirror is pivoted about its axis 26. i

As will appear at a later point, drum 25 is rotated in a counterclockwise direction as viewed in FIG. 1 during operation of the copying machine. An appropriate drive is provided forattaining desired pivotal movement of mirror 23 about its axis 26 in correspondence with the rotary movement of drum25. For this purpose I have typically illustrated a drive 36 which includes a rack 37 engageable with teeth 38 formed on a segment gear 39 which is rigidly connected to drum 25 for rotation therewith. The rack 37 is connected at one end to a spring 40 which is affixed at 41 to the frame of the machine, while the other end of the rack is connected to a tooth flexible timing belt 42 which extends about a gear 43 (of nonuniform radius) rigidly secured to mirror shaft 27, to turn gear 43 and the mirror about axis 26 in a predetermined relationship with respect to the longitudinal movement of rack 37. The opposite end of the timing belt is connected through a spring 44 to a stationary portion 45 of the frame of the machine. The teeth 38 on gear 39 extend about only a portion of the periphery of the gear, so that on each revolution of drum 25, the rack moves longitudinally through a predetermined range of movement and then is spring returned to an original setting after the teeth of gear 39 i move out of engagement with the rack. Thus, a predetermined pivotal movement of mirror 23 and rapid return pivotal movement is attained for each revolution of drum 25. The illustrated mechanisms for actuating the mirror pivotally and along axis 24 are of course only shown as possible typical arrangements, and may be supplanted by any other convenient type of drive.

Drun 25 is of a type adapted to receive and carry an electrostatic image of the subject matter on sheet 14. More particularly, this drum has an outer layer or coating 47 formed of a suitable semiconductor, such as selemium, with this layer being carried about and in close and continuous contact with a layer 48 of a highly conductive metal, such as aluminum, copper, steel, or the like. The drum is mounted by appropriate bearings. 49 for rotation about a horizontal axis 50 parallel to the pivotal axis of mirror 23. A suitable motor represented at 51 contained within housing 11 drives drum 25 at a uniform rate about axis 50 during operation of the mechanism, and typically in a counterclockwise direction as viewed in FIG. 1. As the semiconductor surface material 47 on drum 25 approaches the location of slit 20 in wall 19, the semiconductor material passes an electrical charging unit 52 which gives the entire semiconductor layer an initial charge of a predetermined character. As this charged material passes slit 20, the optical image of sheet 14 which is aimed through the slit by optical system 21 illuminates different portions of the semiconductive material differently, to locally discharge different regions differently in correspondence with the illumination thereof, and in a pattern corresponding to the pattem of the markings on sheet 14. This electrostatic charge pattern is then utilized to apply a corresponding electrostatic pattern to a second parallel drum 53 which ultimately prints visible images on a series of copy sheets 54 advanced by a conveyor 55 at the underside of drum 53. Once the electrostatic image has been applied to the first drum 25, it remains on that drum through a series of revolutions of drum 25, to print a series of the copy sheets 54 from the single initial image. During these subsequent revolutions of drum 25, the charging unit 52 is deenergized, lamps 15 are turned off, and a shutter 125 operated by an actuator 126 automatically closes slit 20, so that the charge pattern on drum 25 remains until the last of the selected number of copies has been printed.

The second drum 53 is mounted by appropriate bearings 153 to turn about a horizontal axis 56 which is parallel to the horizontal axis 50 of drum 25. Motor 51 drives drum 53 in a clockwise direction as viewed in FIG.v 1, and in timed relation to the rotation of upper drum 25 so that the closely proximate portions 57 of the drums move at a common linear speed. As seen best in FIG. 2, the drum 53 has a semiconductive layer 58 typically formed of selenium or the like and capable of acquiring an electrostatic charge pattern corresponding to that which has previously been discussed as produced on selenium layer 47 of drum 25. At the radially inner side of the electrostatically chargeable layer 58, drum 53 has a transparent cylindrical layer or portion 59, through which light from an axially elongated lamp 60 is directed outwardly against the inner surface of layer 58. An opaque stationary cylindrical member 61 within the drum passes light from lamp 60 to selenium layer 58 through only a single axially elongated slit 62 in element 61 at a location directly opposite the most closely proximate portions 57 of the two drums. The spectral emission and intensity of the lamp 60 should be matched to the photoconductive and absorptive characteristics of the semiconductive layer 58 so as to permit the required charge transfer to the outer surface of layer 58 during the period of illumination while at the same time causing layer 58 to be opaque to the radiation from lamp 60 and thereby prevent the passage of light through layer 58 to surface 47 of drum 48. Thus, any tendency for discharge of layer 47 by that light from lamp 60 is prevented. At its opposite ends, drum 53 may carry two highly electrically conductive annular bands or rings 64 of copper, aluminum, or the like, for assisting in conducting partial discharging currents from portions of the selenium layer 58 illuminated by lamp 60.

As the electrostatically chargeable layer 58 of drum 53 advances toward the location 57 in FIGS. 1 and 2, a precharging unit 65 gives layer 58 an initial electrical charge of a predetermined character. When each portion of layer 58 reaches the location 57, it is in very close proximity to layer 47 of drum 25 and is momentarily illuminated by lamp 60 through slit 62 and thereby rendered conductive to allow localized discharging of the layer 58 to a condition determined electrostatically by the charge which is present on layer 47 of drum 25. That is, at each location at which layer 47 of drum 25 has a positive charge, that charge will induce a corresponding negative charge in the closest portion of layer 58 of drum 53, or vice versa. During the instant in which a particular elongated region of layer 58 of drum 53 is illuminated, current can flow through that region to set up charges in a pattern corresponding to the electrostatically charged pattern of the opposed portion of drum 25. As soon as that portion of layer 58 of drum 53 moves out of the illuminated area, conduction ceases in that region and the charges in that region are thereby frozen in a pattern corresponding to the charge pattern on drum 25. This action continues progressively about the entire periphery of drum 53 so that it is given a charge pattern corresponding to the optical pattern on sheet 14. After passing the location 57, the surface of drum 53 passes a toner applying unit 66, which applies toner to the out surface of the very thin opaque dielectric layer 58, with that toner being retained in a pattern corresponding to the electrostatic charge pattern on layer 58, and being ultimately transferred onto one of the sheets 54 by the electrical attraction of an electrostatic transfer unit 67 at the underside of belt 55. As the sheet 54 moves leftwardly carrying the toner, a heating unit 68 fuses the toner in place to render the image on the sheet permanent. A conventional brush 69 removes excess toner from drum 53 after passing sheet 54, to prepare the drum for the next successsive cycle of operation.

The machine may be controlled by a conventional start switch represented at 70 in FIG. 1, which switch acts when pressed by an operator to commence operation of the apparatus under control ofa timer 71, which may be adjusted at 72 to regulate the number of copies to be produced. Timer 71 controls the operation of motor 51, lamps 15, charging unit 52, shutter 125, a copy sheet feed unit represented at 153, and other portions of the apparatus to attain the cycle of operations discussed below.

To trace the operation of the equipment through one complete cycle, assume that it is desired to make a predetermined number of copies of the single original 14. The operator sets timer 71 for the desired number of copies, places the original M in position over window 13, and then presses start button 70 to commence operation of the equipment. When button 70 is presssed, timer 71 may first illuminate lamps 15, and energize motor 51 to commence timed rotation of drum 25 in a counterclockwise direction and drum 53 in a clockwise direction. At the same time, this rotation of the drums causes corresponding pivotal movement of mirror 23 about its axis 26 by virtue of the previously discussed drive through rack 37 and the associated parts of FIG. 3. As different portions of drum 25 approach slit 20, they are precharged by electrical charging unit 52, and are then partially optically discharged in a pattern corresponding to the image on sheet 14 and in accordance with the portions of the image of sheet 14 which are projected through slit 20. The pivotal scanning movement of mirror 23 is so timed as to form a cylindrically curved electrostatic image of sheet 14 on the periphery of drum 25. As each portion of drum 25 reaches the lowermost point 57 in its travel, it comes into very close proximity with layer 58 of drum 53, and during the instant of illumination by lamp 60, causes development of an image pattern on drum 53 corresponding to the image pattern on drum 25. Toner is applied to this image on drum 53 at 66, is transferred to one of the sheets 54 at 67, and is fused on the sheet at 68, with ultimate discharge of the copy sheets to the pick-up location 73 at a side of the housing. After one revolution of drum 25, timer 71 automatically deenergizes lamps l5 and charger 52, and closes shutter 125, to allow continued rotation of drum 25 without loss of the applied electrostatic image on drum 25. After such deenergization of the lamps and unit 52, the motor continues to drive the drums and the feed unit 153 through a number of revolutions of drum 53 corresponding to the number of copies for which control 72 has been set. On each such revolution of drum 53, an electrostatic charge pattern is again applied to drum 53, and particularly its layer 58, in correspondence with the pattern present on drum 25, and toner is again applied to drum 53 and transferred from it to a next successive sheet 54, with fusion of the toner at 68 and ultimate delivery of the sheet to discharge location 73. Thus, the desired number of copies are all formed from the single image produced by one exposure on drum 25. When the selected number of copies have been produced, timer 71 automatically stops the operation of motor 51 and the rest of the equipment in preparation for a next successive cycle.

To now discuss in somewhat greater detail the scanning movement of mirror 23, it may be noted that in conventional equipment of the type utilizing a pivoting mirror of this type it is necessary to shape the top viewing window 13 arcuately about the pivotal axis of the mirror, in order that the distance from the mirror to each of the scanned portions of the sheet 14 may remain the same through the entire scanning operation; In the present apparatus, however, by shifting mirror 23 along optic axis 24 of lens 22 and slit 20, by virtue of the engagement of cam 33 with backup roller 35 as previously discussed, I effect an automatic timed adjustment which enables the sheet 14 to be placed in a horizontal position as illustrated. This shifting movement of the mirror is so controlled and predetermined that, for each angular setting of the mirror, the total length of the light path from drum 25 along optic axis 24 to the mirror, and then from the mirror to the por tion of sheet 14 which is in that particular setting being imaged in slit 20, is the same as the corresponding light path length for all other angular settings or positions of the mirror. Stated differently, the light path from drum 25 through slit 20 to the portion of sheet 14 which is being imaged in slit 20 remains constant for all settings of the mirror. Similarly, the portion of this light path from lens 22 to the sheet 14 also remains constant for all settings of the mirror. With this relationship the portion of the image being projected through slit 20 is at all times in focus on drum 25.

To define the above discussed relationship by mathematical formula, reference may be made to a central position of the mirror in which it is so inclined as to image in slit 20 the portion of sheet 14 which is directly vertically above the pivotal axis of the mirror. Thus, in this position, light follows a shortest possible path directly downwardly to the mirroralong the line (which is perpendicular to the plane of sheet 14), and then 7 rightwardly and downwardly along optic axis 24 to slit 20 and drum 25. If the distance along line from the plane of the paper 14 to optical axis 24 is d, then:

t is the angle between the optic axis and the plane of sheet 14; 0 is the angle of inclination between the normal to the mirror and the axis 24.

The disclosed apparatus is also constructed to effect another type of automatic compensation for the nonarcuate positioning of sheet 14 with respect to the pivotal axis of the mirror. As will be understood, since different portions of sheet 14 are located different distances from the pivotal axis of the mirror, the rate of angular scan of the mirror on the sheet tends to be faster at the center of the sheet than at its ends (where the mirror to sheet radial distance increases). To compensate for this effect and assure formation of a linear image on drum25, l preferably so vary the rate of pivotal movementof the mirror with respect to the rate of rotary movement of the drums as to attain a uniform rate of scan of the mirror within the plane of sheet 14. This may be attained by any convenient type of non-uniform drive between the drums and the mirror, but in the illustrated arrangement is typically achieved by given gear 43 the previously mentioned nonuniform radius, so designed as to pivot the mirror at a predetermined nonuniform rate calculated to produce the desired compensation. Mathematically, the optimum result is achieved when the following relation is maintained:

d0/dS [(sin 26 cos t sin t cos sin t) 2d(1 sin t)] where:

dO/dS is the rate of rotation of the mirror plane with respect to the linear passage of the photosensitive surface of drum past slit 20 for l:l optical conjugates and the other symbols have the same significance discussed hereinabove.

While a certain specific embodiment of the present invention has been disclosed as typical, the invention is of course not limited to this particular form, but rather is applicable broadly to all such variations as fall within the scope of the appended claims. For instance, one or both of the two photosensitive units of the apparatus may be planar instead of in roller form as shown, and

if both are planar the charge induction on the second.

surface may be accomplished simultaneously over its entire area by a uniform pulse' illumination of that whole area.

i claim:

1. A copy machine comprising an optical system for viewing a sheet to be copied and projecting an image thereof onto a photosensitive surface, said optical system including a mirror mounted for essentially pivotal movement about an axis in a relation scanning said sheet to be copied, and means for shifting said mirror essentially transversely of said axis in timed relation to the pivotal movement thereof.

2. A copy machine as recited in claim 1, including an electrostatically chargeable unit having said photosensitive surface formed thereon, there being an elongated slit at one location about the periphery of the drum through which said optical system directs an image of said sheet.

3. A copy machine as recited in claim 1, in which said optical system includes a projection lens interposed optically between said mirror and said photosensitve surface.

4. A copy machine as recited in claim 1, including means for receiving said sheet to be copies in a substantially flattened condition for viewing by said optical system, said shifting means being operable to move the mirror transversely of said axis in a direction and to an extent compensating for the nonarcuate disposition of said flattened sheet about said pivotal axis of the mirror.

5. A copy machine as recited in claim 1, including an electrostatically chargeable rotary drum having said photosensitive surface formed thereon, there being an elongated slit through which said optical system directs a partial scanning image of said sheet to be copied onto a localized portion of said drum as it turns, and a drive connection between said drum and said mirror for turning the drum about its axis in correspondence with rotary movement of the drum, said shifting means including a cam structure which pivots with the mirror and shifts it transversely of the pivotal axis of themirror as the latter pivots. r

6. A copy machine as recited in claim 1, in which said optical system includes a lens, an electrostatically chargeable rotary drum having said photosensitve surface formed thereon, there being an elongated slit through saich lens directs a partial scanning image along a predetermined optical axis onto said drum, said shifting means being operable to shift said mirror along said optical axis in accordance with the formula:

y K[d( l sin t)/(sin 20 cos I sin t cos 20 sin where:

d is the shortest path distance from the mirror to the sheet being copied;

y is the distance from said lens to said mirror along the optical axis;

K is the optical object distance;

t is the angle between the optical axis of the lens and the plane of the sheet being copied;

0 is the angle of the optical axis to a line normal to the mirror;

7. A copy machine comprising an optical system, having an optic axis, for viewing a sheet to be copied and projection an image thereof onto a photosensitive surface; said optical system including a mirror mounted for essentially pivotal movement about a pivotal axis, in a relation scanning said sheet to be copied, means for pivoting said mirror at a nonuniform rate at least partially compensating for a nonarcuate relationship of said sheet with respect to the pivotal axis of the mirror; and means for shifting said mirror transversely of its pivotal axis in timed relation to the pivotal movement of the mirror.

8. A copy machine comprising a unit having a photosensitve surface and moving at a predetermined rate; an optical system, having an optic axis, for viewing a sheet to be copied and projecting an image thereof onto said photo-sensitive surface; said optical system including a mirror mounted for essentially pivotal movement about a pivotal axis in a relation scanning said sheet to be copied; and means for pivoting said mirror at a nonuniform rate at least partially compensating for a nonarcuate relationship of said sheet with respect to the pivotal axis of the mirror; said last mentioned means pivoting said mirror at a rate:

d/dS -[(sin 26 cos tsin t cos sin t)'/2d (l sin t)] where:

0 is the angle of inclination between the normal to the mirror and the optic axis to said unit;

I is the angle between said optic axis and the plane of said sheet;

dO/dS is the rate of pivotal movement of the mirror plane with respect to linear movement of said unit for 1:1 optical conjugates.

Q. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series ofsuccessive of successive of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, and means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said first unit being a rotary electrostatically chargeable drum, said first mentioned means including an optical projection system for viewing said sheet to be copied and projecting a partial image thereof onto a localized portion of said drum, and means forming an elongated slit through which said partial image passes to the drun, said optical projection system including a mirror which reflects light from said sheet to be copied and pivots about an axis in timed relation to the rotation of said drum to scan the sheet to be copied and produce a scanning image thereof through said slit, and means for shifting said mirror es sentially transversely of said axis in timed relation to the pivotal movement thereof.

10. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being an electrostatically chargeable drum which at one location about its periphery is in close proximity to said first unit, and means for illuminating said drum at said location of close proximity to said first unit and thereby rendering it electrically conductive to assume a charge pattern corresponding to the charge pattern on said first unit.

11. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being a rotary drum having an electrostatically chargeable layer whose outer surface is movable into close proximity with said first unit at a predetermined location, and means at the radially inner side of said electrostatically chargeable layer for illuminating said layer at said location of close proximity to said first unit.

12. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a seris of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being a rotary drum having an electrostatically chargeable layer whose outer surface is movable into close proximity with said first unit at a predetermined location, means at the radially inner side of said electrostatically chargeable layer for illuminating said layer at said location of close proximity to said first unit, and a nonrotating light shield within said drum containing a slit through which light from said last mentioned means passes to said electrostatically chargeable layer.

13. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being a rotary drum having an electrostatically chargeable layer whose outer surface is movable into close proximity with said first unit at a predetermined location, and means at the radially inner side of said electrostatically chargeable layer for illuminating said layer at said location of close proximity to said first unit, said drum having a transparent layer radially inwardly of said electrostatically chargeable layer and passing light radially outwardly thereto.

14. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remaino the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said first unit being an electrostatically chargeable first drum, said first mentioned means including an optical projection system for scanning said sheet to be copies and projecting a moving image thereof onto said first drum through an elongated slit, said second unit being a second drum mounted to turn in timed relation to the first drum and having an electrostatically chargeable layer receivable in close proximity to the first drum at a predetermined location about the periphery of the second drum, means for charging said electrostatic layer of the second drum in advance of its arrival at said location of close proximity, and means for illuminating said said printing means include means for applying a toner to said second drum beyond said location of close proximity, means for electrostatically moving said toner from said second drum onto said copy sheets, and

means for fusing the toner on said copy sheets III I t 

1. A copy machine comprising an optical system for viewing a sheet to be copied and projecting an image thereof onto a photosensitive surface, said optical system including a mirror mounted for essentially pivotal movement about an axis in a relation scanning said sheet to be copied, and means for shifting said mirror essentially transversely of said axis in timed relation to the pivotal movement thereof.
 2. A copy machine as recited in claim 1, including an electrostatically chargeable unit having said photosensitive surface formed thereon, there being an elongated slit at one location about the periphery of the drum through which said optical system directs an image of said sheet.
 3. A copy machine as recited in claim 1, in which said optical system includes a projection lens interposed optically between said mirror and said photosensitve surface.
 4. A copy machine as recited in claim 1, including means for receiving said sheet to be copies in a substantially flattened condition for viewing by said optical system, said shifting means being operable to move the mirror transversely of said axis in a direction and to an extent compensating for the nonarcuate disposition of said flattened sheet about said pivotal axis of the mirror.
 5. A copy machine as recited in claim 1, including an electrostatically chargeable rotary drum having said photosensitive surface formed thereon, there being an elongated slit through which said optical system directs a partial scanning image of said sheet to be copied onto a localized portion of said drum as it turns, and a drive connection between said drum and said mirror for turning the drum about its axis in correspondence with rotary movement of the drum, said shifting means including a cam structure which pivots with the mirror and shifts it transversely of the pivotal axis of the mirror as the latter pivots.
 6. A copy machine as recited in claim 1, in which said optical system includes a lens, an electrostatically chargeable rotary drum having said photosensitve surface formed thereon, there being an elongated slit through saich lens directs a partial scanning image along a predetermined optical axis onto said drum, said shifting means being operable to shift said mirror along said optical axis in accordance with the formula:y K -( d( 1 -sin t)/(sin 2 theta cos t - sin t cos 2 theta - sin t)) where: d is the shortest path distance from the mirror to the sheet being copied; y is the distance from said lens to said mirror along the optical axis; K is the optical object distance; t is the angle between the optical axis of the lens and the plane of the sheet being copied; theta is the angle of the optical axis to a line normal to the mirror.
 7. A copy machine comprising an optical system, having an optic axis, for viewing a sheet to be copied and projection an image thereof onto a photosensitive surface; said optical system including a mirror mounted for essentially pivotal movement about a pivotal axis in a relation scanning said sheet to be copied, means for pivoting said mirror at a nonuniform rate at Least partially compensating for a nonarcuate relationship of said sheet with respect to the pivotal axis of the mirror; and means for shifting said mirror transversely of its pivotal axis in timed relation to the pivotal movement of the mirror.
 8. A copy machine comprising a unit having a photosensitve surface and moving at a predetermined rate; an optical system, having an optic axis, for viewing a sheet to be copied and projecting an image thereof onto said photo-sensitive surface; said optical system including a mirror mounted for essentially pivotal movement about a pivotal axis in a relation scanning said sheet to be copied; and means for pivoting said mirror at a nonuniform rate at least partially compensating for a nonarcuate relationship of said sheet with respect to the pivotal axis of the mirror; said last mentioned means pivoting said mirror at a rate: d theta /dS -((sin 2 theta cos t - sin t cos 2 theta -sin t)2/2d (1 - sin t)) where: theta is the angle of inclination between the normal to the mirror and the optic axis to said unit; t is the angle between said optic axis and the plane of said sheet; d theta /dS is the rate of pivotal movement of the mirror plane with respect to linear movement of said unit for 1:1 optical conjugates.
 9. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series ofsuccessive of successive of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, and means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said first unit being a rotary electrostatically chargeable drum, said first mentioned means including an optical projection system for viewing said sheet to be copied and projecting a partial image thereof onto a localized portion of said drum, and means forming an elongated slit through which said partial image passes to the drun, said optical projection system including a mirror which reflects light from said sheet to be copied and pivots about an axis in timed relation to the rotation of said drum to scan the sheet to be copied and produce a scanning image thereof through said slit, and means for shifting said mirror essentially transversely of said axis in timed relation to the pivotal movement thereof.
 10. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being an electrostatically chargeable drum which at one location about its periphery is in close proximity to said first unit, and means for illuminating said drum at said location of close proximity to said first unit and thereby rendering it electrically conductive to assume a charge pattern corresponding to the charge pattern on said first unit.
 11. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being a rotary drum having an electrostatically chargeable layer whose outer surface is movable into close proximity with said first unit at a predetermined location, and means at the radially inner side of said electrostatically chargeable layer for illuminating said layer at said location of close proximity to said first unit.
 12. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a seris of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being a rotary drum having an electrostatically chargeable layer whose outer surface is movable into close proximity with said first unit at a predetermined location, means at the radially inner side of said electrostatically chargeable layer for illuminating said layer at said location of close proximity to said first unit, and a nonrotating light shield within said drum containing a slit through which light from said last mentioned means passes to said electrostatically chargeable layer.
 13. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remains the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic pattern on said second unit, said second unit being a rotary drum having an electrostatically chargeable layer whose outer surface is movable into close proximity with said first unit at a predetermined location, and means at the radially inner side of said electrostatically chargeable layer for illuminating said layer at said location of close proximity to said first unit, said drum having a transparent layer radially inwardly of said electrostatically chargeable layer and passing light radially outwardly thereto.
 14. A copy machine comprising a first electrostatically chargeable unit, means for applying to said unit an electrostatic charge in a pattern corresponding to the markings on a sheet to be copied, a second electrostatically chargeable unit receivable in close proximity to said first unit and adapted on a series of successive cycles of operation to be charged repeatedly by said first unit in a pattern corresponding to a single charge pattern on said first unit which remaino the same for said series of cycles, means operable on said series of cycles to print electrostatically onto a series of copy sheets a repeating printed pattern corresponding to the repeating electrostatic patteRn on said second unit, said first unit being an electrostatically chargeable first drum, said first mentioned means including an optical projection system for scanning said sheet to be copies and projecting a moving image thereof onto said first drum through an elongated slit, said second unit being a second drum mounted to turn in timed relation to the first drum and having an electrostatically chargeable layer receivable in close proximity to the first drum at a predetermined location about the periphery of the second drum, means for charging said electrostatic layer of the second drum in advance of its arrival at said location of close proximity, and means for illuminating said layer at said location of close proximity to give said layer a charge pattern corresponding to that of said first drum.
 15. A copy machine as recited in claim 14, in which said electrostatically chargeable layer of the second drum is opaque, said second drum having a transparent layer radially inwardly of said electrostatically chargeable layer and through which said illuminating means direct light radially outwardly against the electrostatically chargeable layer at said location of close proximity.
 16. A copy machine as recited in claim 15, in which said printing means include means for applying a toner to said second drum beyond said location of close proximity, means for electrostatically moving said toner from said second drum onto said copy sheets, and means for fusing the toner on said copy sheets 